1.
Resistance
Dr. Asif Anas
Director
Genomia Diagnostics
Research Pvt. Ltd.
New Delhi

2.
Classification antibiotic resistance mechanisms
1. On the bases of gene
2. On the bases of action
On the bases of gene
i. Innate drug resistance mechanisms
ii. Acquired drug resistance mechanisms
a. By accruing mutation in gene
b. By accepting drug resistance gene

3.
On the bases of action
i. Preventation of drug access to target
a. Reduced permeability
b. Increase the activity of efflux pump
ii. Change in antibiotic target
a. Modification (Protection) of drug target
b. Mimicry of drug target
iii. Direct modification of antibiotics
a. Inactivation of antibiotics by transfer of chemical group
b. By hydrolysis
iv. Epigenetic drug tolerance

4.
i. Presentation of drug access to target
a. Reduced permeability
• The outer membranes of Gram negative bacteria work as a permeable
barrier in inhibit penetration of antibiotic.
• Outer-membrane porin proteins were used by hydrophilic antibiotics to
cross the outer membrane by diffusing.
• In this case bacteria reduced their membrane permeability by changing
their porins with more-selective channels.
• These more selective channels are the result of mutation in gene
encoding channel.

5.
(Blair et al., 2015)

6.
Increase the activity of efflux pump
• Intrinsic resistance Gram-negative bacteria flush out antibiotic by
bacterial efflux pumps that lead to bacteria escape from antibiotic.
• In this case these efflux pumps overexpress their activity and confer high
levels of resistance to previously useful antibiotics.
• Overexpress efflux pumps can transport a large number of structurally
dissimilar substrates and become multidrug resistance (MDR) efflux
pumps.
• There is large number of MDR efflux pumps already discovered and new
MDR pumps is reporting continuously.
• Ex. fuaABC in Stenotrophomonas maltophilia, mdeA in Streptococcus
mutans, lmrS in S. aureus and kexD in K. pneumonia

7.
ii. Change in antibiotic target
a. Modification (Protection) of drug target
• 23S rRNA ribosomal subunit of Gram-positive bacteria targeted by
linezolid (the first oxazolidinone antibiotic).
• The 23S rRNA ribosomal subunit have multiple allele, it bacteria acquire
mutation in one of these copies and alter the antibiotic target, provide
resistance from antibiotic than recombination between homologous allele
take place which increase population of bacteria harboring mutant allele.
• Without mutation into target gene bacteria can modify their target protein
to provide resistance against antibiotic.
• For example, the erythromycin ribosome methylase (erm) family of
genes methylate 16S rRNA and alter the drug-binding site, thus
preventing the binding of macrolides, lincosamines and streptogramins

8.
(Blair et al., 2015)

9.
Mimicry of drug target
• This type of resistance mechanisms can be seen in fluoroquinolones. The
fluoroquinolones are synthetic antibiotics, can restrict the growth of
microorganisms by inhibit the transcription, DNA replication, and repair.
• The mfpA gene in mycobacteria was first recognised showing low-level
resistance to fluoroquinolones.
• MfpA protein has maximum similarity to pentapeptide repeat proteins.
The structure of mfpA protein of mycobacteria is nearly similar to the
double helix DNA, and have cyclic pentapeptides coiled as right handed
helix with same width as of DNA.
• It is reported that DNA structure was mimicked by mfpA protein to
deviate the fluoroquinolones.

10.
iii. Direct modification of antibiotics
By enzymatic hydrolysis
• The hydrolysis of antibiotic by bacterial enzyme is a major resistance
mechanism that has been prevalent since the use of first antibiotic
penicillin which is a β-lactam antibiotic hydrolyzed by β-lactamase.
• Till date, numbers of enzymes have been reported that can modify and
degrade antibiotics of different classes, including β-lactams, phenicols,
aminoglycosides and macrolides.
• The enzyme β-lactamases exist in diverse range and can degrade dif-
ferent antibiotics within the same class; for example penicillins,
carbapenems, clavams, cephalosporins and monobactams.

11.
(Blair et al., 2015)

12.
Inactivation of antibiotics by transfer of chemical group
• Bacterial enzyme added the chemical group on antibiotic and alters its
original structure. Structurally changed antibiotic lose their activity due
to hindrance with target.
• There many antibiotic resistance enzyme which can transfer various
chemical groups including acyl, nucleotidyl, phosphate and ribitoyl
groups.
• Aminoglycoside-modifying enzymes provide resistance to bacteria by
adding hydroxyl and amide groups to aminoglycoside group of
antibiotics.
• Aminoglycoside-modifying enzymes are classified in three major groups:
phosphotransferases, acetyltransferases and nucleotidyltransferases.

13.
iv. Epigenetic drug tolerance
• Epigenetic drug tolerance different kind of drug resistance tool, noticed in
mycobacteria generally found latent or relapsed TB cases.
• This type of drug resistance nullify the antibiotic activity when
mycobacterial cell enter in dormant condition in case of latent or relapsed
TB.
• Mycobacterial cell slow down its growth in latent or relapsed TB cases by
minimise their metabolic activity. So there is no or less requirement of
metabolites or protein to the cell.
• Thus, there is no lethal inhibition in dormant bacterium even when
antibiotics targets their object.
• Treatment of persister cells in case of latent infections is much challenging as
than treatment of dividing cells in active tuberculosis.

14.
Causes of Antimicrobial (Drug) Resistance
1. Inappropriate Use
• Selection of resistant microorganisms is exacerbated by inappropriate use
of antimicrobials. Sometimes healthcare providers will prescribe
antimicrobials inappropriately, wishing to placate an insistent patient
who has a viral infection or an as-yet undiagnosed condition.
2. Inadequate Diagnostics
• More often, healthcare providers must use incomplete or imperfect
information to diagnose an infection and thus prescribe an antimicrobial
just-in-case or prescribe a broad-spectrum antimicrobial when a specific
antibiotic might be better. These situations contribute to selective
pressure and accelerate antimicrobial resistance.

15.
3. Hospital Use
• Critically ill patients are more susceptible to infections and, thus, often
require the aid of antimicrobials. The extensive use of antimicrobials and
close contact among sick patients creates a fertile environment for the spread
of antimicrobial-resistant germs.
4. Agricultural Use
• Scientists also believe that the practice of adding antibiotics to agricultural
feed promotes drug resistance. There is still much debate about whether
drug-resistant microbes in animals pose a significant public health burden.
5. Gene Transfer
• Microbes also may get genes from each other, including genes that make
the microbe drug resistant. Bacteria that have drug-resistant DNA may
transfer a copy of these genes to other bacteria. Non-resistant bacteria receive
the new DNA and become resistant to drugs.